Handheld and/or wireless barcode scanners (i.e., indicia readers) are typically powered by a rechargeable energy storage unit (RESU). Traditionally the RESU has used a battery as its energy storage component. Batteries are optimized to provide energy for prolonged periods of continuous operation, which suits the needs for most electronic devices (e.g., laptops, cellphones, etc.). Barcode scanners, however, typically operate in a different fashion. Active periods are often followed by periods of non-operation. As a result, other energy storage components may be considered for powering the barcode scanner. A super capacitor (i.e., ultra-capacitor, double layer capacitor, etc.), for example, may be suitable energy storage component for an RESU.
The super capacitor stores energy via a static charge rather than an electrochemical reaction or other process. As a result, the charging/operating characteristics required for super-capacitor RESUs is different from battery RESUs. For example, a super-capacitor can be charged more quickly than a lithium-ion (Li-ion) battery. The super capacitor may be charged/discharged many times and typically has a longer service life than a Li-ion battery. As a result, super capacitors may be used for barcode scanning applications, which may require short-term power bursts followed by quick charging periods.
The charging process (i.e., the currents/voltages applied over time) of a super capacitor are different from a Li-ion battery. For example, the super capacitor may accept larger charge currents. The super capacitor cannot be overcharged and does not require the detection of a full-charge since the charge current stops flowing when the super capacitor has reached its charge limit. A Li-ion battery, on the other hand, requires carful control of charging current/voltage, and care should be taken to stop charging when the battery has reached its charge limit. In addition, safety mandates that the temperature of a Li-ion battery be monitored and the charge/use of the Li-ion battery discontinued when the battery becomes excessively warm.
Either a Li-ion battery or a super capacitor may be used to as the energy storage component in a barcode-scanner's RESU. It is desirable for an RESU to fit/operate in any barcode-scanner/charger without regard to the type of energy storage component used by the RESU. Additional mechanical keying features added to an RESU to indicate the RESU type (i.e., super-capacitor type or battery type) add additional costs and may cause user frustration. One detectable difference between a super-capacitor-type RESU and a battery-type RESU (e.g., Li-ion type RESU) arises from the temperature sensor (e.g., thermistor) required for temperature control in the battery-type RESU.
Traditionally, RESUs have an electrical connector (e.g., pin, tab, contact, etc.) specifically for monitoring temperature. Typically, this connector (i.e., thermistor pin) is connected to a thermistor within the RESU. Temperature may be detected by sensing the thermistor's resistance (i.e., the terminal resistance at the thermistor pin) since the thermistor's resistance varies with temperature (e.g., 10K ohms at room temperature). For a super-capacitor RESU, however, this pin may be shorted since temperature control is unnecessary. As a result, a super-capacitor RESU and a Li-ion RESU may be visually identical but will have different terminal resistances at their respective thermistor pins.
Therefore, a need exists for a charger that can detect what type of RESU is being charged based on the terminal resistance at the RESU's thermistor pin and then adjust the charging process based on the type of RESU detected.